Index: guestbook.module
===================================================================
--- guestbook.module	(Revision 362)
+++ guestbook.module	(Arbeitskopie)
@@ -322,6 +322,14 @@
   if ($account->uid > 0 && $account->uid == $user->uid) {
     user_save($user, array('guestbook_visited' => time()));
   }
+  
+  // fetch missing parameters
+  if (is_null($op)) {
+    $op = arg(3);
+  }
+  if (is_null($op_id)) {
+    $op_id = arg(4);
+  }
 
   // Delete or comment an entry
   $comment_entry = $sql_where = '';